Demountable gun for cathode ray tubes



Jan. 19, 1960 n. w. MAYER ETAL DEMOUNTABLE GUN FOR CATHODE RAY TUBES Filed May 8, 1956 TIIITEJ.

7 2 22 Ram m M mmm wm vwfl w W 2 Y B United States Patent iiice 2,922,062 Patented Jan. 19, 1960 nnrreuNrAeLu GUN non carrronn Donald N. Mayer, Colonia, and Albert M. Skellett, Madison, Ni, assignors to Tang-Sol Electric Inc a corporation of Delaware Application May 8, 1956, Serial No. 583,547

2 Claims. (Cl. 31382) Our present invention relates to cathode ray tube manufacture, and more particularly to the manufacture of electron guns for television picture tubes and com prises a novel gun structure which permits the gun to be salvaged for reuse after the picture tube has failed for any reason. Although the electron guns, particularly of color television picture tubes, represent a substantial fraction of the cost of the tube, for example, over one half of the cost of the bulb, guns have heretofore been so constructed that salvage thereof has been impractical.

When air is admitted to a picture tube by removal of the button stem, the emissive material of the cathode is impaired but the gun is not otherwise damaged. In conventional gun constructions the cathode can not be removed from the grid cup and replaced, either by a new cathode or by the former cathode resurfaced with emissive material. In the gun construction of the present invention, the cathode may be accurately replaced without damage to the gun, thus making the gun reusable after mounting on a new stem. in the new gun construction as in conventional guns, the precision spacing of the cathode to grid is maintained by a grid cathode spacer ring positioned between the base of the grid cup and a ceramic spacer within which the cathode is firmly fixed, a retainer ring engaging the opposite surface of the ceramic spacer and holding the ceramic spacer in contact with the grid-cathode spacer ring. In the conventional construction the retainer ring cannot be removed without destruction of the grid cup. In the construction of the present invention the retainer ring and grid cup are so constructed that the ring may be removed from the cup without impairing the utility of the grid cup for future use.

For a better understanding of the invention and of specific embodiments thereof, reference may be had to the accompanying drawing of which:

Fig. l is a sectional view of the cathode-grid assembly portion of a cathode ray gun embodying the invention;

Fig. 2 is a partial side view of the assembly of Fig. 1 showing the manner in which the retainer ring may be removed from the grid cup; and

Fig. 3 is a sectional view of a cathode-grid assembly of a gun representing another embodiment of the invention.

In Fig. l on a greatly exaggerated scale, is shown a portion of the gun of a cathode ray tube comprising a conventional cathode cylinder 2, ceramic disc 4 supporting the cathode, a grid cup 6 within which the disc and cathode are mounted, a grid-cathode spacer ring 8 between the disc and base of the grid cup and a retaining ring 10 which holds the disc in engagement with the spacer ring. The cup 6 is supported between rods 12 of glass or the like by means of metal pins 14 each of which is welded at one end to the grid cup wall and embedded at its other end in a rod 12. It will be understood the rods 12 as in conventional gun construction,

support the other electrodes (not shown) of the gun. In accordance with the invention, the retaining ring 10 and grid cup 6 are so constructed that the ring may be removed from the cup without impairing the serviceability of either for reuse and also so constructed as to minimize vibration and thereby avoid generation of microphonic noise.

In the embodiment of the invention illustrated in Figs. 1 and 2, mating screw threads are rolled into the Walls of the cup and retaining ring to insure vibrationless contact between the cup and retaining ring while permitting the ring during assembly to be brought up into firm engagement with the surface of the ceramic disc. After assembly the retaining ring is locked in position by a single weld, indicated at 16, near the open end of the grid cup. Thus, when the gun is to be salvaged for reuse it is only necessary, as indicated in Fig. 2, to remove the small amount of material at the weld, as by means of a simple notching tool. The retaining ring 1% may then be unscrewed from the cup, the cathode removed and replaced after resurfacing with emissive material, the retaining ring screwed back into place within the grid cup and spot welded to the cup at a new location. Because of the mating rolled screw threads in the walls of the retaining ring and grid cup it is not necessary to weld the two elements together at more than one location nor is it necessary to unite the elementsv at locations near the ceramic disc. In prior art constructions wherein these elements had smooth oylindrical walls, welding at numerous points adjacent the ceramic disc was necessary to insure locking of the retaining ring and to avoid vibrations of the part of the ring between the disc and location of the welds. In such prior art construction, removal of the retaining ring thus necessitated destruction of the cup.

In the embodiment of the invention illustrated in Fig. 3, the retaining ring is constructed of spring material and is in the form of a split ring '10 while the grid cup 6 is formed with an internal annular groove 18 into which the ring 10 seats. The groove 18 is so located that the ring 10 when seated therein engages the ceramic disc 4 and holds it in engagement with the grid-cathode spacer ring 8. An opening 20 is provided in the wall of the groove 18 to permit insertion of a suitable tool (not shown) for ejection of the ring 10' from the groove, when the gun is to be demounted for replacement or resurfacing of the cathode.

The invention has now been described with reference to two specific embodiments. Other constructions involving vibrationless mounting of a removable retaining ring within a grid cup to permit salvage of a cathode ray tube gun within the scope of the accompanying claims and in accordance with the invention will occur to those skilled in the art.

The following is claimed:

1. In a grid cathode sub-assembly for an electron gun wherein the cathode, mounted in a ceramic disc, is spaced from the aperture in the grid cup by means of a cathodegrid spacer, the improvement comprising an annular retainer member engaging the grid cup walls in the neighborhood of the ceramic disc and holding the disc in engagement with the spacer, said retainer member having an end annular wall adapted to engage the disc and a cylindrical wall with a helical groove therein mating with a similar groove in the wall of the grid cup, the wall of said retainer member and the wall of the grid cup being spot welded together adjacent the edges thereof remote from the disc and at a single location only, whereby said retainer member is removable and replaceable without impairment of the walls of the grid cup in the neighborhood of the ceramic disc.

2. In a cathode sub-assembly for an electron gun ,inengagement with the spacer, said grid cup being provided with an annular groove in the neighborhood of .the disc and said retainer member comprising a split ring adapted to seat in said groove, the grid cup Wall having an aperture intersecting 'said circular groove for access to the ring when the sub-assembly is to be dismantled. r

References Cited in the file of this patent UNITED STATES PATENTS West July 10, 1917 Singer July 24, 1928 Guan Oct. 16, 1945 Moss July 12, 1949 Shekels Oct. 2, 1951 .Pohle Jan. 15, 1952 Grifliths Aug. 7, 1956 

